Habitat associations and life histories of odonata in riverine wetlands of the Willamette Valley, Oregon

Graduation date: 2003This thesis explored the distributions and life histories of dragonflies and\ud damselflies (Insecta: Odonata) of the riverine wetlands of the Willamette Valley\ud in western Oregon, USA. Odonate species distributions were characterized over\ud two seasons in the autumn of 2000 and the spring of 2001-at twenty-seven\ud wetlands located throughout the valley. Distributions of nymphs and adults were\ud compared with wetland habitat conditions that may affect odonate diversity.\ud Odonate nymph and adult distributions were analyzed through\ud Hierarchical Agglomerative cluster analysis (HA). HA identified discrete\ud clusters of sites based on the distributions of species in the genera Aeshna,\ud Erythemis, Lestes, Libellula, Pachydiplax, Sympetrum and Tramea. To identify\ud habitat associations with odonate species, nymph and adult data were analyzed\ud by Non-metric Multidimensional Scaling (NMS). NMS revealed that odonate\ud distributions are associated with site hydrology, water depth and temperature, the\ud presence of large emergent plants (e.g. Typha latifolia), the presence of fish, and\ud surrounding landcover. These data will provide guidance for wetland managers\ud in the use of odonates as indicators of wetland health.\ud To further examine the relationship between odonate species and their\ud wetland habitats, quantitative life history data for the 27 odonate species were\ud analyzed to determine functional associations between species attributes and the environments in which they are found. Oviposition location, presence of a\ud resting egg, over-wintering life stage, nymphal foraging strategy and adult flight\ud season were subjected to NMS, to determine biological similarities between\ud species occupying particular locations. Life history patterns correlated strongly\ud with hydrology. Analysis of sites by odonate species ricimess found a\ud relationship between richness and site hydrology, but failed to explain the\ud distribution of several species associated with wetlands that dry during part of\ud the year. We conclude from our results that species-level life history data are\ud essential for explaining odonate distributions.\ud We determined that the presence of odonate species in a wetland is\ud indicative of habitat condition, that analysis of odonate distributions at the\ud species level is necessary to understand habitat associations, and that analysis of\ud life-history attributes provides a functional understanding of odonate\ud distributions that measurements of species richness or the distributions of generaor families alone cannot explain